1. Field of the Invention
This invention generally relates to a dither algorithm, and more particularly to a dynamic dither algorithm for a four-time resolution refinement of an image, both spatially and temporally.
2. Description of Related Art
In conventional dither algorithm for 6-bit source drivers of thin-film-transistor liquid crystal display (TFT LCD) panel, an 8 to 6-bit resolution dither function is provided. The dither function manages to mimic 256 colors, being supposed to be synthesized to 8-bit, with only 6-bit. Two algorithms are mainly provided in a conventional scheme.
One is 2-dimension (2D) static dither, and the other is 3-dimension (3D) dynamic dither. Generally, in both algorithms, each block of 2×2 pixels is observed on an image. For the 2D-dither algorithm, it offers constant pattern for “carry” among the observed blocks on the image and lower quality is obtained, yet the 3D-dither is more flexible in providing “carry” pattern, and improves the defects to 2D-dither. However, 3D-dither has to be well designed so that moving pixels or dithered edges are avoided for an image of frames. Detail descriptions of “carry” and an observed block are provided as follows.
Referring to FIG. 1 for a brief description of 2D-dither algorithm. An 8 to 6-bit dither is exemplary, yet a 10 to 8-bit, 8 to 6-bit, or 6 to 4-bit dither are performed similarly. Basically, the concept of dither is to add one “carry” (one “carry” is equal to the quantity of 4, in a 2-bit LSBs case) to the valid 6-bit MSBs at proper position and proper time. Firstly, with the 2-bit LSBs being 00, no carry is generated for the 6-bit MSBs among the four pixels of an observed block, to which the pixel under operation belongs. Secondly, with the 2-bit LSBs being 01, one of the four pixels is added a carry for the 6-bit MSBs. Furthermore, with the LSBs being 10, two of the four pixels are added a carry for the 6-bit MSBs, thus an average extra pixel value of 2 is obtained. Lastly, with the LSBs being 11, three of the four pixels are added a carry for the 6-bit MSBs, so that an average pixel value of 3 is obtained. According to foregoing description, a 2D-dither algorithm is easy to implement, for carry is only added in spatial domain. This exemplary 2D-dither method is shown in the table of FIG. 1.
In 2D-dither algorithm, every single pixel is of the same value of every frame with the same input image, constant patterns, such as dot moiré (when the LSBs are 10) or quad dot (when the LSBs are 01 or 11) is observed on the screen. Thus this static is seldom used for dithering colors.
3D-dither algorithm, being enhancement of 2D-dither, is described herein in a conventional scheme. Besides dither in spatial domain, 3D dither also provides dithering in temporal domain. With dynamic dither on the screen, moving pixels are observed, especially on a fast response panel. The basic observed unit of the conventional 3D-dither method is as well 2×2 bock, including 4 pixels. With each the LSBs 2-bit being 10, the conventional 3D-dither method provides moving pixels moving left and right at the first horizontal scan line, and right and left at the second horizontal scan line. With each the LSBs being 01 or 11, the conventional 3D-dither method has three basic approaches, described as follows.
The first conventional method for 3D-dither is that the moving pixel goes upper-left, upper-right, lower-right, and lower-left for sequential frames for all the 2×2 blocks. The second conventional method for 3D-dither is that the moving pixel goes upper-left, lower-right, lower-left, and upper-right for sequential frames for all the 2×2 blocks. The third one is that the moving pixel goes upper-left, lower-left, upper-right, and lower-right for sequential frames for all the 2×2 blocks. The tables in FIGS. 2A to 2C depict foregoing descriptions of the conventional 3D scheme therein.
The general drawbacks of 3D-dither occur in the three conventional methods. There is no problem for the LSBs being 10. Yet with the LSBs being 01, horizontal lines move when the first method (FIG. 2A) or the second method (FIG. 2B) is inspected. Besides, with all the 2×2 blocks moving the same way, dithered edges occur at the horizontal gray-256 pattern when the first method or the third method (FIG. 2C) is applied. Thus, drawbacks to 3D dither are inspected in the three conventional methods.